1. Field of the Invention
This invention relates to a process for producing a polyester, and also relates to a method of recycling hemicellulose and cellulose.
2. Related Background Art
Conventional general-purpose plastic products are polymeric compounds synthesized chiefly from petroleum resources. More specifically, polymeric compounds such as polyester, polystyrene, nylon, polyethylene, polyvinyl chloride, polyimide and polycarbonate are, in almost all cases, produced from monomers obtained using petroleum as a raw material.
The petroleum, however, is a limited resource, and is foreseen to become depleted before long. Accordingly, a technique is earnestly desired by which general-purpose plastic products are produced from new materials substitutive for the petroleum, i.e., renewable materials.
Meanwhile, the recycling of wastepaper or the like is put forward with an increase in demand for paper, which is due to the spread of personal computers and office automation machinery, the use of paper containers and so forth. However, the number of times paper can be recycled is limited, because the lengths of paper fibers decrease, and it is greatly questioned how wastepaper that is no longer recyclable or the like be disposed. On the other hand, from the viewpoint of effective utilization of resources, it is sought to utilize wastepaper or the like by means other than thermal recycling. Paper is composed primarily of cellulose. Thus, the focus of the studies is on decomposition of this cellulose so as to be reused.
Cellulose is produced in an amount of 109 to 1011 tons per year, and is used in a large quantity for extensive purposes, such as structural materials, fillers, food additives and further adhesives or the like. With such use, waste cellulose also increases year by year.
Hemicellulose, which is present in vegetable tissues in a proportion of 20 to 30%, also finds its way into paper without being removed in the course of the manufacture of pulp. Its quantity can reach as much as about 20%. Thus, when the effective utilization of wastepaper is taken into account, the effective utilization of the hemicellulose component cannot be ignored. Also, hemicellulose discarded in the course of the manufacture of cellulose has been increasing along with the increase in demand for paper.
Meanwhile, starch is a polymeric compound formed by dehydrating polymerization of D-glucose, and is an important polysaccharide, inclusive of cellulose. The starch is produced from potatoes, sweet potatoes, corn and so forth. Its yield (the crop of corn) in the whole world is about four to five hundred million tons per year. It is produced in the largest quantity among natural resources, and is a renewable resource. Accordingly, starch is a promising new substitute resource for petroleum, if general-purpose plastic products can be manufactured from starch.
As techniques by which the waste cellulose is decomposed and reused, known are, e.g., a method in which hydrocarbons, such as methane and ethane, are derived from cellulose (Japanese Patent Application Laid-open No. 5-213778) and a method in which alcohols are produced from cellulose (Japanese Patent Application Laid-open No. 11-299479).
As techniques in which the waste hemicellulose is utilized, studies are made on food additives (Japanese Patent Applications Laid-open No. 5-17503 and No. 5-43470), foaming agents (Japanese Patent Application Laid-open No. 5-244880), sizing agents for fiber texturing (Japanese Patent Application Laid-open No. 5-263367), cosmetic materials (Japanese Patent Application Laid-open No. 6-157238), fiber materials (Japanese Patent Application Laid-open No. 6-220213) and so forth.
Incidentally, production of thermosetting resin materials from lignocellulose is disclosed in Japanese Patent Application Laid-open No. 6-126715, which are manufactured for use in adhesives in view of physical properties.
In order to deal with future increases in these wastes, a novel technical development is necessary to enable more efficient recycling. Accordingly, the present inventors have taken note of the fact that the increasing wastes are pulp, paper, waste starch and so forth on the one hand, and the fact that plastic materials substitutive for the petroleum are sought on the other hand, and have studied the production of plastics from saccharides. If plastics can be produced from saccharides, useful industrial produces can be provided using abundant starting materials. Also, the depletion of petroleum resources can be avoided and any environmental pollution caused by wastes can be eliminated.